1. Field of the Invention
The present invention relates to reticulated coatings and, in particular, to reticulated coatings that exhibit enhanced lubricity or xe2x80x9cslipxe2x80x9d with respect to both dry and damp surfaces and are suitable for use in medical device products.
2. Description of the Related Art
Thin polymer films are used in the manufacture of a variety of medical device products, such as medical gloves, condoms, wound dressings, catheters, angioplasty balloons and the like. In the case of medical gloves, such as surgeon""s gloves or examination gloves, the ease of donning the glove is an important consideration, as too is the breathability of the base polymer, to reduce the build-up of moisture within the glove. Consequently, such gloves usually require the application of powders or coatings which confer anti-frictional properties. Ultimately, however, the barrier properties of gloves and condoms are of primary concern and it is essential that the application of any coating should not reduce these properties. An additional requirement of such a coating is that it must adhere strongly to the underlying substrate and must be able to be applied to a variety of substrate materials without degrading the intrinsic properties of the substrate material. Soft elastomeric films are of particular value as coatings (and also as xe2x80x9cfilm articlesxe2x80x9d, such as condoms) but are characterised by the tacky or xe2x80x9cblockyxe2x80x9d nature of the film surfaces when dry, which can lead to problems of unwanted adhesion when products are stored or dried in bulk. In order to overcome this, products are frequently treated with a dusting powder, such as corn starch, to render the surface tack-free. However, post-operative adhesions and granulomas have become increasingly associated with the presence of such powders on invasive medical devices, whilst undesirable allergic hypersensitivity reactions to latex used in medical gloves may be exacerbated by the presence of such powders. Consequently, the alternative of using a powder free, anti-block coating to prevent adhesion and confer slip properties has particular value.
U.S. Pat. No. 4,642,267, for example, discloses a hydrophilic blend comprising an organic solvent-soluble, thermoplastic polyurethane and a hydrophilic poly(N-vinyl lactam) which is slippery in aqueous environments and may be used as a low-friction coating for catheters. The blend is prepared using conventional melt-blending techniques or by dissolving the components in a solvent, which is subsequently evaporated to yield the blend. In the latter case, however, this document discloses that the solvent must be capable of dissolving both polymer components in a single-phase solution and that the relative volatilities must be such that, at no point during evaporation and drying, must the solution tend to precipitate either polyurethane or poly(N-vinyl lactam) or an association complex of these polymers which may have different solubility characteristics than either material by itself.
Anti-block coatings prepared by conventional methods often require elaborate and expensive manufacturing procedures and the properties of the coatings so obtained are often inferior to those of dusting powders. It is an object of the present invention to overcome some of the aforementioned disadvantages by providing a novel method of forming a reticulated coating that has good xe2x80x9cslipxe2x80x9d properties when damp or dry.
Accordingly, in a first aspect of the invention, there is provided a method of forming a reticulated coating on a substrate, comprising providing an agglomerate dispersion of a pre-formed first polymer in a polar liquid carrier on a surface of the substrate, and evaporating the liquid carrier to form the coating.
In one embodiment, the reticulated coating is adapted to render the surface of the substrate substantially tack-free or anti-blocking when dry, so as to ensure that articles that are provided with the coating, such as medical gloves, do not adhere to each other. Preferably, the reticulated coating is substantially free of substances capable of causing undesirable allergic hypersensitivity reactions, which is particularly important if the coatings are to be used for medical applications. In another embodiment, the coating has an Ra value of at least 0.5 xcexcM.
In the context of the present invention, the term xe2x80x9cRa valuexe2x80x9d is understood to refer to the arithmetic mean of the absolute departures of the roughness profile of the surface from the mean line, in accordance with its usual meaning in relation to engineering surfaces (see, for example, ISO 4287/1:1997, and also ISO 11 562). Similarly, Rq or RMS is the root mean square parameter corresponding to Ra, whilst Rmax is the maximum peak to valley height of the profile in the assessment length. The first polymer may be any material capable of forming a film coating when wet but is generally a thermoplastic, a thermosetting resin or an elastomer and will already have been polymerized before it is used to prepare the agglomerate dispersion, i.e., the agglomerate dispersion will not usually be obtained as the product of an in situ polymerization reaction. Preferably, the thermoplastic, thermosetting resin or elastomer is selected from the group consisting of polythene, polypropene, polymethylpentane, polystyrene, polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polymethyl methacrylate, polyacrylonitrile, polyacrylamide, aromatic polyesters, polycarbonates, polyamines, polytetrafluoroethene, alkyd resins, unsaturated polyesters, urea-methanal polymers, polyureas, melamines, polyurethanes, polyamides, epoxy resins, polyethene oxide, polyphenylene oxide, polyacetals, polyaldehydes, phenolic resins, polysulphones, natural rubbers, polyisoprene, polybutadiene, polychloroprenes, butyl rubbers, styrene-butadiene rubbers, acrylonitrile-butadiene rubbers, polysulphides, silicones and mixtures thereof. In the context of the invention, the phrase xe2x80x9cmixtures thereofxe2x80x9d should be understood to include co-polymers of any of the preferred monomers, as well as simple mixtures of the fully polymerised compounds. It is especially preferred that the thermoplastic, thermosetting resin or elastomer is selected from the group consisting of polyurethanes, neoprene, latex, styrene acrylic emulsions and nitriles. Most preferably, the first polymer is a polyurethane or a natural rubber, such as latex. Polyurethanes are especially preferred, particularly those prepared from polyesterpolyols, polyetherpolyols, polycarbonatepolyols and mixtures of these. The polar liquid carrier may be any liquid carrier capable of developing an electrical charge and forming an agglomerated dispersion with the first polymer. Such liquid carriers may include but are not limited to water, dilute mineral acids, methanol, ethanol, diethylether, dimethylsulphoxide and dimethylsulphone. Preferably, the liquid carrier is aqueous. In one embodiment, the agglomerated dispersion of the first polymer is applied to the surface of the substrate after it has been formed, preferably by spraying the agglomerated dispersion onto the substrate or by dipping the substrate in the agglomerated dispersion. In an alternative embodiment, the agglomerate dispersion is formed in situ on the surface of the substrate, preferably by applying a colloidal dispersion of the first polymer to the surface of the substrate and by inducing agglomeration, for example, by electrolysis. In a preferred embodiment, the agglomerate dispersion of the first polymer is formed from a colloidal dispersion of the first polymer in the polar liquid carrier. In this embodiment, the colloidal dispersion preferably contains micelles of the first polymer having an average particle size in the range of 0.1-100 nm, preferably 1-75 nm, and especially about 50 nm.
Preferably, the reticulated coating is lubricious and confers enhanced slip with respect to both dry and damp surfaces. In any of these embodiments, the average size of the particles in the agglomerated phase may be in the range of 0.1-100 xcexcm, preferably 0.5-25 xcexcm, most preferably 1-15 xcexcm. In a preferred embodiment, the agglomerate dispersion may also comprise a second polymer, preferably preformed. The second polymer may be any compound that confers suitable properties on the final coating but will generally be selected from the group consisting of polyolefins, polyamines, polyamides, polysaccharides, polyamino sugars, polynucleotides, phospholipids and mixtures thereof. In an embodiment, the second polymer is capable of interacting with the polar liquid carrier in such a way that the first polymer is induced to form an agglomerate dispersion in the polar liquid carrier. For example, the second polymer may be capable of forming an intimate network with the polar liquid carrier, such as a hydrogel or a colloidal solution, thereby reducing the ability of the polar liquid carrier to interact with the first polymer and causing the first polymer to form an agglomerate dispersion in the polar liquid carrier. Preferably, the second polymer forms a colloidal suspension with the polar liquid carrier. In another embodiment, the polar liquid carrier is aqueous and is capable of hydrogen bonding with the second polymer, such that the free energy of the polar liquid carrier is reduced, thereby increasing the tendency of (possibly micelles of) the first polymer to agglomerate.
Preferably, the second polymer is selected from the group consisting of poly(aromatic alkenes), poly(meth)acrylates, glucosamine-containing polymers, galactosamine-containing polymers, alginates, pectins, polypeptides, poly(N-vinyl lactams), cellulose, cellulose derivatives, lecithins, cephalins, sphingomyelins and mixtures thereof. Most preferably, the second polymer is soluble in water and is selected from the group consisting of polystyrene, polymethyl methacrylate, polyvinylpyrrolidone, poly(N-vinyl caprolactam), hydroxymethylcellulose, hydroxyethylcellulose, pectin esterified from citrus fruit, sodium alginates, chitosan, chitin, poly(N-acetyl-D-glucosamine), co-polymers of polyvinylpyrrolidone with 2-dimethylaminoethylmethacrylate, co-polymers of polyvinylpyrrolidone with styrene, co-polymers of polyvinylpyrrolidone with acrylic acid, polyethylenimine, ethoxylated polyethylenimines, N-propionyl substituted linear polyethylenimines, 1-[N[poly(3-allyloxy-2-hydroxypropyl)]-2-aminoethyl]-2-imidazolidinone, polyacrylamides, co-polymers of polyacrylamide with acrylic acid, poly(2-ethyl-2-oxazoline), L-xcex1-phosphatidylcholine dioctanoyl, and mixtures thereof. Polyvinylpyrrolidone and hydroxyethylcellulose are especially preferred, as the use of these components produces coatings with excellent but quite distinct surface characteristics and properties.
The agglomerate dispersion may be formed by any suitable method but will generally be formed in the presence of an electrolyte, such as a salt. In this embodiment, the salt is preferably a metal salt or an ammonium salt selected from the group consisting of fluorides, chlorides, bromides, sulphates, sulphites, sulphides, hydrogencarbonates, carbonates, nitrates, nitrites and mixtures thereof. Of these, sodium chloride is especially preferred, although many other salts, such as lithium chloride or calcium chloride, may be equally effective. The salt may be present in any amount effective to induce agglomeration of the first polymer but is preferably present in an amount of from 0.01 g/l to 100 g/l, particularly 0.05 g/l to 50 g/l, more preferably 0.1 g/l to 10 g/l, and especially 6.0 g/l, based on the total volume of the agglomerate dispersion. Optionally, the agglomerate dispersion may also be formed in the presence of a surfactant, especially one which helps to solubilize the first polymer or helps to disperse the first polymer throughout the solution. Surfactants suitable for this purpose may be any amphoteric, ionic, cationic and non-ionic surfactants that are suitable for use on skin and other tissues and include but are not limited to long-chain fatty acids, quaternary ammonium compounds, betaines and suteines, amine oxides, sulfosuccinates and isothionates. Preferably, the surfactants are selected from the group consisting of alkyldimethylammonium betaines, coco aminopropyl betaine, N-lauryl or N-cetyl pyridinium salts, hydroxyethylheptadecenylimidazoline salts, hexadecyltrimethylammonium chloride, benzalkonium chloride and hexadecyl pyridinium chloride. In a preferred embodiment, an aqueous colloidal dispersion of the first polymer is added to an aqueous salt solution containing the second polymer dissolved therein. In this case, the colloidal dispersion contains micelles of the first polymer component having an average particle size in the range of 0.1-100 nm, preferably in the range of 1-75 nm, and especially about 50 nm.
In an embodiment of the invention in its first aspect, the coated substrate is washed after the liquid carrier has been evaporated so as to remove unwanted residues, such as salt used to form the agglomerate dispersion. Depending upon the nature of the second polymer however, the washing step may also remove substantially all of the second polymer from the coating itself. This is especially noted where the second polymer is hydroxyethylcellulose. Alternatively, the second polymer may be substantially undissolved by the washing step and remains present in the coating, as observed when the second polymer comprises polyvinylpyrrolidone. In an especially preferred embodiment of the invention, a third polymer is applied to the surface of the substrate, preferably as a film or thin layer, prior to providing the agglomerate dispersion. The third polymer may comprise a thermoplastic, a thermosetting resin or an elastomer, such as those used for the first polymer and, preferably, the third polymer is the same as the first polymer. The third polymer may be applied to the surface of the substrate in the form of a solution or a suspension, possibly by dip-coating or by spraying, and may be dried before the agglomerate dispersion is provided on the surface. Preferably, the third polymer is dried at a temperature of 15-150xc2x0 C. for a period of 1-60 minutes, more preferably at a temperature of 50-100xc2x0 C. for a period of 1-30 minutes, and especially at a temperature of about 80xc2x0 C. for a period of about 5-10 minutes. However, the exact temperature and duration of the drying step required to give good coating characteristics may be determined by routine experimentation. It has been observed that, depending upon the drying time and the degree of xe2x80x9cwetnessxe2x80x9d of the film of the third polymer the agglomerate dispersion of the first polymer interacts with the surface of the substrate to a greater or lesser degree giving markedly different properties to the final product. The precise mechanism by which this occurs is not fully understood but is believed to be determined by the hydrophilic/hydrophobic nature of the third polymer, as well as the potential for hydrogen bonding. In a further embodiment, the reticulated surface of the coated substrate is treated with a surfactant to further increase the damp slip properties of the substrate. Surfactants suitable for this purpose may be any amphoteric, ionic, cationic and non-ionic surfactants that are suitable for use on skin and other tissues and include but are not limited to long-chain fatty acids, quaternary ammonium compounds, betaines and suteines, amine oxides, sulfosuccinates and isothionates. Preferably, the surfactants are selected from the group consisting of alkyldimethylammonium betaines, coco aminopropyl betaine, N-lauryl or N-cetyl pyridinium salts, hydroxyethylheptadecenylimidazoline salts, hexadecyltrimethylammonium chloride, benzalkonium chloride, hexadecyl pyridinium chloride and silicones/organosiloxane polymers.
In a second aspect of the invention, there is provided a reticulated coating obtained by a method according to the invention in its first aspect. Preferably, the coating so obtained is reticulated or xe2x80x9croughenedxe2x80x9d and has a reticulated component particle size in the range of 1-25 xcexcm and an average roughness in the range of 1-10 xcexcm, preferably in the range of 2-12 xcexcm with an average roughness of about 5 xcexcm.
In a third aspect of the invention, there is provided an article having a reticulated coating according to the invention in its second aspect. Preferably, the article is a medical device, such as a condom, a medical glove, a wound-dressing, a catheter, an angioplasty balloon, a stent, a valve, or a surgical suture.
Thus, the present invention provides an anti-block coating system which may be applied to a variety of substrate materials, including glass, metal, ceramics, PVC, natural rubber latex, polyurethane, nylon, polyethylene and mixtures or composites of any of these. Such anti-block coatings can be applied to a medical device, such as a surgeon""s glove, by applying a thin layer of the agglomerated dispersion onto the device, by for example spraying or dipping, and then heating the device in an oven to drive off the aqueous component of the coating system. This results in a multitude of agglomerate particles adhered onto the medical device surface. The adhered agglomerates may be conjoined to form a continuous but reticulated surface, alternatively the agglomerates may form a discontinuous coating with uncoated areas of substrate. The continuity of the coating, the size of the agglomerates and the resulting roughness of the reticulated surface may be manipulated within certain limits in order to modify the anti-block properties and lubricity of the coating. Furthermore, the formulation of the coating system may be modified to give agglomerates with a range of morphologies exhibiting different adherence, anti-block and lubricity properties.